Ok i have had this 94 dodge ram for about 2 years it has a 5.9 liter engine. My dads workers were driving it which means alot of **** on it broke or got **** up actually it wasnt in to bad of shape compared to some of the others but it sat for about a year the engine barely ran it needed a valve job. so instead we just got a new remanufactured engine and we redid the interior and the paint and got new rims and tires and some stuff. First question i have is what temperature should it be at it was at the 200 all the time but my fan clutch was bad and the fan was on all the time. today i got my fan clutch fixed and now the temperature is all over the scale it goes up to almost the red then goes down. so im thinking i need a new thermostate what do you guys think? also my brakes are like **** and the abs lite is always on it seems like the back brakes arennt working sometimes and sometimes they do i have noidea what thats about. also i am about to change my differential fluid and there is no like drain plug on the bottom should i just get a new gasket and take the cover off to drain it? also should i use synthetic in it or no? and also there is a metal pipe that comes out of my water pump and it goes into a hose i think its like the heater core return and they told me to change the o ring because it was leaking but i pulled it out and there is no o ring slot or anything...where is the o ring supposed to go on the tube or in the water pump im thinking the tube needs an o ring slot and i should just get a new tube. wow i typed alot i just signed up for this site and dont know much about dodges hopefully you guys can help me out thanks alot bye.

 

first off your post is hard to read... break it up a bit.

swapping the rear diff fluids can be done 2 different ways... one is with a vacuum pump thru the fill plug and the other is to pop off the rear cover. I do the rear cover because you can see what's on the magnet on the bottom of the diff and get it really clean.
Use redline 75w90 gear oil in there.

swap out the t-stat with a 180 deg one. drill a small hole in the valve so that air can escape past it and prevent air lock when filling it up. you may already have an air pocket in there from what you describe.

the return line for the heater has an o-ring on it, when you put it in, there is a raised section of the tube that will press up against the o-ring and seal it.

Check out the DIY forum for how-to's if your doing the work yourself and are unsure of anything.